A major effort in the coming year will be in the area of propagation of gnotobiotic animals. These will be used in the experiments proposed for the study of cellular and humoral immune responses of Peyer's patch and lamina propria cells. Further studies are planned on the lymphoid tissue of the murine large intestine using the oral Listeria model as well as the oral Yersinia enterocolitica and Salmonella models. The loose ends of the studies on the thymic dependence of the secretory IgA system and the efficacy of H3-cytidine labelling of Peyer's patch lymphocytes will be tied up. BIBLIOGRAPHIC REFERENCES: Carter, P.B. 1975. Spread of enteric fever bacilli from the intestinal lumen. Microbiology - 1975 edited by D. Schlessinger. p. 182-187. American Society for Microbiology, Washington, D.C. Carter, P.B., 1975. Animal model: oral Yersinia enterocolitica infection of mice. Am. J. Path. 81:703-706.